High performance engines, supported by engine manufacturers, are much in demand by auto racing enthusiasts as well as by individuals who simply desire higher performance than available from original equipment manufacturer (O.E.M.) engines. However, high performance engines are generally not available to those race teams, or individual car owners, who are not directly associated with major manufacturers of automotive engines, auto components or lubricant makers. Thus, low budget race teams, and individuals, must depend on standard production engines that can be modified, preferably at low cost.
Engine manufacturers do not, as a general rule, mass produce high performance race engines. The high performance engines that are manufactured require specialized tooling and are, therefore, relatively expensive. As a result, auto racing enthusiasts will generally modify production engines with components that are available from specialized dealers, or manufacturers, at a reasonable cost. Engine components which are most commonly modified are the head, the valve train components (e.g., the cam shafts), the pistons and the throw rods, and those components are readily available from smaller specialty manufacturers. However, the cylinder head, and its components, are the most popular performance increasing products.
High performance cylinder head designs generally incorporate specially shaped chambers that serve to facilitate, or increase: fuel/air mass flow; fuel/air mixing; and, compression. As such, the head chambers have utilized hemispherical, or wedge, shapes, in order to provide sufficient room for the operation of the valves which must move linearly into and out of the combustion chamber at an angle relative to the piston head. The valve size, as well as the degree and the rapidity with which they open and close, have a definite effect on the amount of air which can be taken into the cylinders. Because the quantity of the fuel/air mixture which can be ingested into the cylinder to be available within the cylinder during combustion can have a significant affect on the power development and the maximum operating speed of the engine, the valve opening and closing characteristics are given careful attention.
One particularly successful improvement in high performance heads is known from U.S. Pat. No. 4,686,948, which issued to Smith et al on Aug. 18, 1987. The '948 patent is owned by the assignee of the present invention and describes an engine head as having a wedge-shaped combustion chamber with a flat quenching surface. The wedge-shaped combustion chamber described therein results in improved fuel consumption and simultaneous high brake horsepower.
The intake passage of the head described in the '948 patent has a velocity increasing restriction adjacent the inlet valve which improves the flow of atomized fuel and directs it in an even fashion around the inlet valve. The result of this structural arrangement increases the velocity of the incoming fuel charge without deleteriously effecting the volume of incoming air. This patent and others have directed the improvements mainly to the wedge-shaped configuration of the combustion chamber.
U.S. Pat. No. 4,919,092 which issued to Smith et al on Apr. 24, 1990--and which is also owned by the assignee of the present invention--utilizes a metal mass buildup positioned about the inlet valve, in conjunction with an improved intake passage, to draw the fuel/air charge into the chamber in a helical flow pattern. The intake passageway described in the '092 patent is useful in drawing a rich fuel/air mixture through the inlet valve at a location remote from the exhaust valve while introducing a lean fuel/air mixture through that portion of the inlet port that is located in closer proximity to the exhaust valve. This arrangement, of course, is intended to limit the amount of scavenging--i.e.: the fuel passing directly between the inlet and exhaust valve during valve overlap (that period of time during which both the intake and the exhaust valves are simultaneously open).
It is well known that fuel/air mixtures often contain some droplets of fuel which are not properly atomized and which, if delivered to the chamber, will generally be scavenged prior to the compression stroke, thereby limiting the energy available. Another prior art teaching is found in U.S. Pat. No. 5,076,224 which issued to Smith et al on Dec. 31, 1991, and which is also owned by the assignee of the present invention. The '224 patent discloses a high performance head wherein the inlet passage upstream of the intake valve has an arcuate-shaped, rounded boss that is positioned to direct the heavier droplets of fuel toward a heated wall, or floor, of the inlet passage. The fuel droplets will be atomized as they impact the heated wall. The operation of the '224 structure depends on the heat conduction through the walls of the inlet manifold, and to assist with the desired heat transfer, passages are provided through which the exhaust gas may circulate.
The prior art, including the specific patents discussed in the preceding paragraphs, all have the intake and exhaust valves disposed in a coplanar relation. In addition, the center of the valve heads are aligned with a longitudinal plane along the reciprocating axis of the piston when the valves are closed. The valves are disposed at a common angle, generally on the order of about twenty-three degrees ( 23.degree.), relative to the longitudinal plane. This valve angle provides the space necessary to permit the added material that aids in directing the fuel/air mixture during ingress and egress from the combustion chamber.